This invention provides a retrofit substitute for the midsection and the lower unit of a standard outboard motor, having a substitute closed-loop cooling system with an exterior heat exchanger, a substitute oil reservoir, a substitute exhaust system, and a substitute propulsion system having an isolating power-take-off shaft, allowing an existing standard outboard-motor powerhead to be used in conditions not conducive to standard open-loop water cooling, such as shallow-water, muddy-water, obstructed-water, seawater, or corrosive-water conditions.
The reason for this invention is that boats that navigate inland waterways, coastal marshes, and swamps, encounter areas that are shallow, sometimes filled with invasive vegetation, or silted up with mud that is too soft to walk in or use any other sort of vehicle to access. Boats, particularly shallow draft, are the only vehicle practical to access these areas, but outboard motors become useless once they travel outside of channels deep enough for cooling and exhaust systems to work properly. Also the lower unit gearbox section is not designed to deflect obstructions, or was design intended for the rugged use when encountering submerged obstructions such as, mud, logs, sand, etc.
There are boat motors built for use in these areas and situations called shallow water outboards, often times referred to as mud motors. The powerheads used presently are air-cooled engines commonly used on lawn mowers and portable generators and pressure washers. A well known problem is that these engines are very limited in horse power. The highest available horsepower engine in this class is quite low, when compared to conventional outboard motors on the same size and type of boats. The demand for higher horsepower shallow water outboard motors has been present for many years with no solution.
Outboard motors have been in production and use for over 100 years and have become very popular, efficient, and reliable. They are limited though, to clean, deeper channels.
Outboard motors would be a good alternative to the limited horsepower air-engines but they were designed and are built specifically for raw water cooling outboard lower ends. The outboard engine crankshaft has no external shafting. The crankshaft does not extend out of the engine base like the presently used air-cooled engines, and only accepts the driveshaft of its intended mate, the outboard motor lower unit. It is water cooled with its water pump being built into its mate, the lower unit. The outboard-motor powerhead has no exhaust system except for its mate, the conventional lower unit and midsection. The exhaust travels through the midsection and out of the lower unit. This hot exhaust is cooled by raw cooling water after it has been supplied to the powerhead, and exiting the cooling jackets of the powerhead. So while the outboard-motor powerhead is compact, lightweight, and very reliable, it is not considered to be and option for shallow water outboard motors or any other machinery since it was designed and built with the outboard motor midsection and lower unit as a necessary part of the complete operable engine.
The combustion cycle of an engine create torque pulses that momentarily accelerate or decelerate crankshaft operation. This is caused by the firing order, the firing angle and the number of cylinders and the combustion cycle. The stop-start forces applied by torque pulses exert a twisting pressure on the drive train. These torque pulses introduce harmonic excitation forces and cause what is known as torsional vibration in a drive line, such as an outboard motor that does not have a water pump in the driven shaft. The conventional water pump creates a constant load on the outboard drive line eliminating the acceleration-deceleration effect from the engine pulses. Torque pulses ripple through the system as torsional vibrations that cannot be seen or felt like the familiar linear (up-and-down, side-to-side) type of vibration because the forces of action/reaction are distributed across different planes tangential to the drive shaft rather than confined to the same plane. Because torsional vibration is “invisible”, the damage that it causes is often mistakenly attributed to some other cause such as shaft-to-shaft misalignment, improperly specified components, or faulty parts.